What is the integral of sec^2(x) dx?

The integral of sec^2(x) dx is indeed tan(x) + C. This result stems from basic integration rules in calculus concerning trigonometric functions.

The derivative of tan(x) is sec^2(x), which establishes a direct relationship for integration. When you integrate sec^2(x), you essentially reverse the differentiation process, arriving at tan(x). The constant of integration, denoted as C, must be included as antiderivatives are defined up to an arbitrary constant.

This connection between the integral of sec^2(x) and the function tan(x) makes the correct answer straightforward and reinforces the importance of understanding the fundamental derivatives and their corresponding integrals in trigonometry.